Plasmid shuttle vector between Escherichia coli and Brevibacillus

ABSTRACT

The invention provides a plasmid shuttle vector characterized by being replicable in both of bacteria of the genus  Brevibacillus  and  Escherichia coli , and by comprising a promoter capable of functioning in bacteria of the genus  Brevibacillus  and a DNA sequence(s) capable of functioning as a selective marker(s) for  Escherichia coli  and bacteria of the genus  Brevibacillus , and a method of transforming bacteria of the genus  Brevibacillus  using the said plasmid shuttle vector. The plasmid shuttle vector enables the efficient transformation of bacteria of the genus  Brevibacillus . Further, since plasmid shuttle vector pNCMO2 of the invention in particular has a gene expression control region which efficiently expresses and secretes an objective gene in bacteria of the genus  Brevibacillus  but significantly suppresses the expression in  Escherichia coli , a recombinant gene expression plasmid can efficiently be constructed using  Escherichia coli , and it is suited for protein production in bacteria of the genus  Brevibacillus.

TECHNICAL FIELD TO WHICH THE INVENTION BELONGS

The present invention relates to a plasmid shuttle vector between Escherichia coli and bacteria of the genus Brevibacillus and a method of transforming bacteria of the genus Brevibacillus using the plasmid shuttle vector. More specifically, it relates to a plasmid shuttle vector which has a gene expression control region effectively expressing and secreting an objective gene product in bacteria of the genus Brevibacillus but significantly suppressing the expression in Escherichia coli, and which is suited for gene expression in bacteria of the genus Brevibacillus. Further, it relates to a process for producing a protein, characterized by culturing a transformant transformed by the transformation method.

PRIOR ART

Udaka et al. have succeeded in the development of an expression system of a recombinant protein using as a host bacteria of the genus Brevibacillus (separated from the ordinary classification of the genus Bacillus) having excellent characteristics, not found in Escherichia coli and Bacillus subtilis, that a large amount of a protein is secreted extracellularly and an extracellular protease activity is weak (Japan Patent No. 2082727, JP-A 62-201583 (1987), Yamagata, H. et al., J. Bacteriol., 169, 1239-1245 (1987), Shigezo Udaka, Nippon Nogeikagaku Kaishi 61, 669-676 (1987), Takao, M. et al., Appl. Microbiol, Blotechnol., 30, 75-80 (1989), Yamagata, H. et al., Proc. Natl. Acad. Sci., USA 86, 3589-3593 (1989)). Production of α-amylase (Japanese Patent No. 2082727) or human epidermal growth factor (hEGF) (Japanese Patent No. 2787585) by an expression system using bacteria of the genus Brevibacillus as a host, and the like have been so far reported.

Meanwhile, as a plasmid vector useful for gene expression of bacteria of the genus Brevibacillus, for example, pNU200 (Shigezo Udaka, Nippon Nogeikagaku Kaishi 61, 669-676 (1987)), pNH300 (Shiga, Y. et al., Applied and Environmental Microbiology, 58, 525-531 (1992)), pNH400 (Ishihara, T, et al., J. Bacteriol., 177, 745-749 (1995)), pHY700 (JP-A 4-278091 (1992), pHT series plasmids (Japanese Patent No. 2727391) and the like have been so far reported. Especially, the present inventors applied pNY301 and other pNY series plasmids for patent (JP-A 10-295378) as a plasmid vector useful for transformation of bacteria of the genus Brevibacillus.

Problems that the Invention is to Solve

As mentioned above, the secretory production system of proteins using bacteria of the genus Brevibacillus as a host is one of useful systems in production of proteins by genetic recombination. However, a transformation efficiency of bacteria of the genus Brevibacillus is low in comparison to a transformation efficiency of Escherichia coli. Accordingly, there was a defect that construction of recombinant gene expression plasmids using bacteria of the genus Brevibacillus is difficult in comparison to Escherichia coli. For example, in case of using an electroporation method (Takagi, T. et al, Agric. Biol. Chem., 53, 3099-3100 (1989)), a transformation efficiency of Escherichia coli reaches 10¹⁰ CFU/ugDNA. Meanwhile, in case of Brevibacillus choshinensis (Bacillus brevis before; there was a change in taxonomical position in Shida O., et al., Int. J. Syst. Bacteriol., 46, 939-946 (1996)) belonging to the genus Brevibacillus, it was only 10⁷ CFU/ugDNA. Further, it has been known that in case of employing a method except the electroporation method, the transformation efficiency of bacteria of the genus Brevibacillus is more reduced.

Especially, transformation of bacteria of the genus Brevibacillus with a gene encoding a protein having a complex quaternary structure, for example, a gene encoding a protein such as cholera toxin (CT) produced from Vibrio cholerae comprising one A subunit and five B subunits (Clements and Finkelstein, Intect. Immun., 24; 760-769 (1979)) and protein production using the transformant have to date experienced a great many difficulties.

As one of measures to cope with the problems, a method is considered in which a plasmid vector (hereinafter referred to as a “shuttle vector”) replicable also in other host cells easy of a transformation step, for example, Escherichia coli is used, construction of a recombinant gene expression plasmid using the host cells is first constructed and transformation of bacteria of the genus Brevibacillus is further conducted by electroporation or the like using the recombinant gene expression plasmid.

A shuttle vector and a transformation method using the shuttle vector are techniques known to those skilled in the art. For example, with respect to a shuttle vector between Escherichia coli and Bacillus subtilis, JP-A 63-198986 (1988), JP-A 2000-197491 and the like have been reported. Nevertheless, a plasmid shuttle vector utilizable in a transformation procedure by genetic recombination of bacteria of the genus Brevibacillus and in recombinant gene expression with the transformant, and a method of transforming bacteria of the genus Brevibacillus using the said plasmid shuttle vector have been to date unknown.

Means for Solving the Problems

The present inventors have focussed on such usefulness that an objective protein is extracellularly secreted in an expression system using bacteria of the genus Brevibacillus as a host, have seriously considered the necessity for the development of a novel host-vector system that solves the foregoing defects, and have tried to develop a novel plasmid shuttle vector in which Escherichia coli and bacteria of the genus Brevibacillus can be used as a host and which can be used in genetic recombination.

Thus, in order to attain the object, the present inventors have focussed again on the point that especially plasmid vector pNY301 which the present inventors have already applied for patent, among a large number of plasmid vectors, contains a promoter and a secretion signal sequence from Brevibacillus choshinensis HPD31. Based on this plasmid vector pNY301, they have synthesized various DNA sequences by PCR or the like, or cut them out from known sequences, further inserted these DNA fragments into the plasmid vector and confirmed the insertion. Moreover, they have performed confirmation of transformation with the resulting plasmids, confirmation of expression in transformants, and so forth. As a result of performing a huge number of these delicate treatments and operations with trial and error, they have finally succeeded in production of a desired novel plasmid shuttle vector.

The novel plasmid shuttle vector which has been successfully produced in this manner has been introduced into Escherichia coli and bacteria of the genus Brevibacillus, and the resulting bacteria have been cultured. Consequently, replication of the plasmid shuttle vector has been performed in any of the hosts. It has been found that in the recombinant gene product expression using the plasmid shuttle vector, an objective gene is effectively secreted and expressed in bacteria of the genus Brevibacillus, but the expression is significantly suppressed in Escherichia coli. It has been further confirmed that even though a transformant of bacteria of the genus Brevibacillus is not obtained by other known methods, the transformation is enabled with the use of the plasmid shuttle vector. Thus, the invention has been completed.

That is, for solving the foregoing problems, the invention provides a plasmid shuttle vector between Escherichia coli and bacteria of the genus Brevibacillus which is useful for transformation by genetic recombination of bacteria of the genus Brevibacillus and for protein production with the transformant, and a transformation method using the plasmid shuttle vector. Especially, it provides a plasmid shuttle vector having a gene expression control region which efficiently expresses and secretes an objective gene product in bacteria of the genus Brevibacillus, but which significantly suppresses the expression in Escherichia coli, and being suited for gene expression in bacteria of the genus Brevibacillus and for protein production. Further, the invention provides a method of transforming bacteria of the genus Brevibacillus using the plasmid shuttle vector, and a process for producing a protein, characterized by culturing bacteria of the genus Brevibacillus transformed with the plasmid shuttle vector.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a P2 promoter.

FIG. 2 shows a Lac operator sequence.

FIG. 3 shows an SD sequence (SD1).

FIG. 4 shows an SD sequence (SD2).

FIG. 5 shows an R2L6 type modified signal peptide (nucleotide sequence in upper column, and amino acid sequence in lower column).

FIG. 6 shows PCR cloning primer 1.

FIG. 7 shows PCR cloning primer 2.

FIG. 8 shows PCR cloning primer 3.

FIG. 9 shows PCR cloning primer 4.

FIG. 10 shows PCR cloning primer 5.

FIG. 11 shows PCR cloning primer 6.

FIG. 12 shows PCR cloning primer 7.

FIG. 13 shows PCR cloning primer 8.

FIG. 14 shows PCR cloning primer 9.

FIG. 15 shows PCR cloning primer 10.

FIG. 16 shows PCR cloning primer 11.

FIG. 17 shows PCR cloning primer 12.

FIG. 18 shows PCR cloning primer 13.

FIG. 19 shows PCR cloning primer 14.

FIG. 20 shows PCR cloning primer 15.

FIG. 21 shows a restriction map of plasmid shuttle vector pNCMO2.

FIG. 22 shows a process of construction of plasmid shuttle vector pNCMO2.

FIG. 23 shows a continuation of FIG. 22.

FIG. 24 shows a process of construction of recombinant gene expression plasmids pNCMO2BLA and pNC301BLA.

FIG. 25 shows a productivity of E. coli JM109/pNCMO2BLA and E. coli JM109/pNC301BLA.

FIG. 26 is a photo in place of a drawing, showing a halo formability and growth by E. coli JM109/pNCMO2BLA and E. coli MP109/pNC301BLA.

FIG. 27 is a photo in place of a drawing, showing effects of IPTG with respect to BLA expression by E. coli JM109/pNCMO2BLA.

FIG. 28 shows a productivity of BLA by Brevibacillus choshinensis HPD31-S5/pNCMO2BLA and Brevibacillus choshinensis HPD31-S5/pNC301BLA.

FIG. 29 shows a process of construction of recombinant gene expression plasmid pNCMO2CT.

FIG. 30 is photos in place of a drawing, showing a Coomassie Brilliant Blue stain image and a western blotting image of a culture of transformant Brevibacillus choshinensis HPD31-S5/pNCMO2CT.

MODE FOR CARRYING OUT THE INVENTION

The invention is described in detail below.

The plasmid shuttle vector of the invention is a plasmid shuttle vector replicable in both of Escherichia coli and bacteria of the genus Brevibacillus, and comprising a promoter capable of functioning in bacteria of the genus Brevibacillus, and a DNA sequence(s) encoding a selective marker(s) for bacteria of the genus Brevibacillus and Escherichia coli.

The plasmid shuttle vector of the invention is autonomously replicable in Escherichia coli and bacteria of the genus Brevibacillus. Accordingly, a recombinant gene expression plasmid can be constructed by a step such as insertion of a DNA fragment in the plasmid shuttle vector of the invention using Escherichia coli, and further transformation of bacteria of the genus Brevibacillus can be performed using the recombinant gene expression plasmid.

The promoter capable of functioning in bacteria of the genus Brevibacillus, which the plasmid shuttle vector of the invention possesses, is not particularly limited so long as it functions in bacteria of the genus Brevibacillus. It is preferably a promoter from bacteria of the genus Brevibacillus. Especially preferable examples thereof can include promoters contained in an MWP promoter region from Brevibacillus brevis 47 (Bacillus brevis 47 before)(JP-B 1-58950 (1989) and JP-B 7-108224 (1995)) and an HWP promoter region from Brevibacillus choshinensis HPD31 (FERM BP-6863)(Bacillus brevis before; this strain is the same as Bacillus brevis H102 (FERM BP-1087)(JP-A4-278091 (1992) and JP-A6-133782 (1994)), for example, a P2 promoter (Sequence No. 1: FIG. 1).

The plasmid shuttle vector of the invention further comprises a ribosome-binding region (SD sequence) and a DNA sequence encoding a signal peptide for secreting an expression protein (secretion signal sequence) at the 3′-terminus of a promoter functioning in bacteria of the genus Brevibacillus. As the SD sequence, for example, a sequence from an HWP gene expression control region of Brevibacillus choshinensis, such as SD1 (Sequence No. 3: FIG. 3) or SD2 (sequence No. 4: FIG. 4) can be used. As the secretion signal sequence, for example, a signal sequence contained in an HWP promoter region of Brevibacillus choshinensis HPD31 (FERM BP-1087, FERM BP-6863) can be used. As an especially preferable example, a modified HWP signal sequence of R2L6 type or the like (JP-A 7-170984 (1995)) can be mentioned (with respect to this R2L6 type modified signal sequence, its amino acid sequence is shown in Sequence No. 5, and its DNA sequence is shown in Sequence No. 21. Further, both of the sequences are shown in FIG. 5. In the drawing, the upper column shows a nucleotide sequence, and the lower column shows an amino acid sequence).

The plasmid shuttle vector of the invention further comprises the DNA sequence encoding a replication control region necessary for replication in bacteria. With respect to the replication control region, either one common region or different regions may be used for both of bacteria of the genus Brevibacillus and Escherichia coli. The replication control region in bacteria of the genus Brevibacillus comprises a Rep protein gene and an origin of replication. The sequence capable of functioning as a replication control region in bacteria of the genus Brevibacillus is not particularly limited so long as it is contained in a plasmid which is replicated and grown in bacteria of the genus Brevibacillus and is a DNA sequence functioning as a replication control region of a plasmid. As an especially preferable example, a Rep protein gene from plasmid pUB110 and a DNA sequence encoding an origin of replication can be mentioned.

In Escherichia coli, an origin of replication is required as a replication control region. A DNA sequence encoding an origin of replication capable of functioning in Escherichia coli is not particularly limited so long as it is a DNA sequence contained in a plasmid replicated and grown in Escherichia coli and functioning as an origin of replication of a plasmid. Preferable is a DNA sequence containing an ori region functioning as an origin of replication of a plasmid. Especially preferable is a DNA sequence encoding an ori region of plasmid vectors ordinarily used in a genetic recombination manipulation using Escherichia coli, such as pUC series, for example, pUC18, pUC118 and pUC119, and pBR322.

As a DNA sequence encoding a replication control region capable of functioning in both of bacteria of the genus Brevibacillus and Escherichia coli, a replication control region of a plasmid belonging to a pLS1/pE194 plasmid family, which is a replication control region capable of functioning in both of Gram-positive bacteria and Gram-negative bacteria (Del Solar, G. et al., Mol. Microbiol., 8, 789-796 (1993)) can be mentioned. For example, a DNA sequence encoding a replication control region (Sano. K. et al., FEMS Microbiology Letters, 148, 223-226 (1997)) comprising ori, RepA and RepB of plasmid pLA106 from Lactobacillus acidophilus can be used.

With respect to sequences capable of functioning as selective markers for bacteria of the genus Brevibacillus and Escherichia coli, which the plasmid shuttle vector of the invention possesses, one common DNA sequence or different DNA sequences may be used to both of bacteria of the genus Brevibacillus and Escherichia coli. With respect to the sequences capable of functioning as the selective markers, a drug resistance gene can be used. For bacteria of the genus Brevibacillus, for example, a DNA sequence containing a drug resistance gene from bacteria of the genus Brevibacillus and bacteria of the genus Bacillus analogous thereto can be used. Especially preferable examples thereof can include a neomycin resistance gene contained in plasmid vector pNY301(JP-A 10-295378 (1998)) and an erythromycin resistance gene contained in pHT110 (Japanese Patent No. 2727391). Further, for Escherichia coli, for example, a DNA sequence encoding a kanamycin resistance gene, an ampicillin resistance gene, a chloramphenicol resistance gene or the like which is a known drug resistance gene from Escherichia coli is available. Still further, as a drug resistance gene capable of functioning in both of bacteria of the genus Brevibacillus and Escherichia coli, a zeocin resistance gene or the like can be used.

The plasmid shuttle vector of the invention can further comprise a DNA sequence having a function to suppress expression of recombinant gene in Escherichia coli. For example, in case of Escherichia coli having a lacI gene, a lac operator sequence (Sequence No. 2: FIG. 2) from Escherichia coli can be contained in the 3′-terminus of a promoter sequence functioning in bacteria of the genus Brevibacillus.

The plasmid shuttle vector of the invention is novel. For example, pNCMO2 is a plasmid vector having a size of 5,224 bp. A restriction map of pNCMO2 and a nucleotide sequence of its part containing a promoter were shown in FIG. 21. The promoter region of pNCMO2 contains a P2 promoter from an HWP promotor region of Brevibacillus choshinensis HPD31, a lac operator from Escherichia coli, an SD sequence, an R2L6 type modified signal sequence as a secretion signal sequence, a multicloning site and an HS gene (JP-A 9-224677 (1997)) as a terminator. With respect to the multicloning site, PstI, BamHI, SalI, XbaI, XhoI, EcoRI, KpnI, SmaI, ClaI, HindIII sites are available as cloning sites.

Plasmid shuttle vector pNCMO2 contains a DNA sequence encoding a neomycin resistance gene as a selective marker gene for bacteria of the genus Brevibacillus, a Rep protein gene from pUB110 necessary for replication in bacteria of the genus Brevibacillus, a ColE1 ori region as an origin of replication of Escherichia coli and an ampicillin resistance gene as a selective marker gene for Escherichia coli.

In the construction of plasmid shuttle vector pNCMO2 in the invention, pNY301, pNH326, pNU201 and the like are used. Plasmid pNY301 is laid open in JP-A 10-295378 (1998), plasmid pNH326 in Kajino., T., et al., Appl. Environ. Microbiol., 66, 638-642 (2000), and pNU201 in Udaka, S. et al., Methods in Enzymology, 217, 23-33 (1993) respectively, and these are known plasmids. Other plasmids which are used in construction of the plasmid shuttle vector of the invention can be procured on the market.

Brevibacillus choshinensis HPD31-S5/pNCMO2 carrying plasmid vector pNCMO2 was internationally deposited on Dec. 12, 2000 in Patent Microorganism Depository of National Institute of Bioscience and Human-Technology, Agency of Industrial Science and Technology, Ministry of International Trade and Industry (the present name: International Patent Organism Depositary, National Institute of Advanced Industrial Science and Technology, AIST Tsukuba Central 6,1-1, Higashi 1-chome, Tsukuba-shi, Ibaraki-ken, 305-8566, Japan), and it is assigned Receipt No. FERM BP-7394.

The host used in construction of the expression plasmid of the invention is not particularly limited so long as it is a strain belonging to Escherichia coli. As an especially preferable example, E. coli JM109 can be mentioned. E. coli JM109 is a known strain which can be procured on the market.

With respect to a method of constructing a recombinant gene expression plasmid from the plasmid shuttle vector of the invention using Escherichia coli, a method based on a standard technology of molecular biology known to a skilled person can be used properly. For example, the method described in Molecular Cloning 2nd ed., A Laboratory Manual, Cold Spring Harbor Laboratory (1989)) is mentioned. The details are described in Examples.

As the host used in the expression of the recombinant gene in the invention, any strain of bacteria of the genus Brevibacillus can be used. Preferable is Brevibacillus choshinensis. Especially preferable examples can include Brevibacillus choshinensis HPD31 (FERM BP-1087, FERM BP-6863), and Brevibacillus choshinensis HPD31-S5 (FERM BP-6623) which is a variant thereof.

As a method of transforming bacteria of the genus Brevibacillus using the shuttle vector of the invention and a recombinant gene expression plasmid constructed with Escherichia coli, a known transformation method known to a skilled person, such as electroporation, can be used.

A medium used in culture of the transformant of the invention contains, as required, a carbon source, a nitrogen source and inorganic salts. Culture may be conducted using a synthetic medium made mainly of saccharide and inorganic salts. In case of using a strain exhibiting auxotrophy, it is advisable to add nutrients required for its growth to a medium. Further, antibiotic, antifoam and the like may be added as required.

With respect to culture conditions, the initial pH of a medium is controlled to from 5.0 to 9.0, preferably from 6.5 to 7.5. The culture temperature is usually from 15° C. to 42° C., preferably from 24 to 37° C., and the culture time is usually from 16 to 360 hours, preferably from 24 to 144 hours. Bacteria of the genus Brevibacillus transformed by the method of the invention thereby produce and accumulate proteins in a culture solution.

After completion of the culture, collection of an objective protein from the culture is enabled by an appropriate combination of protein purification methods known to a skilled person, such as solvent extraction, ultrafiltration, ammonium sulfate fractionation, HPLC, gel filtration chromatography, ion exchange chromatography, affinity chromatography, hydrophobic interaction chromatography, electrophoresis and isoelectric focussing.

EXAMPLES

The invention is illustrated more specifically below by referring to Examples. However, this is illustrative, and the invention is not limited thereto.

Example 1

Construction of Plasmid Shuttle Vector pNCMO2

(1) Construction of Plasmid Shuttle Vector pNC301

Amplification was conducted by PCR with plasmid vector pUC119 as a template using primer 1 (Sequence No. 6: FIG. 6) and primer 2 (Sequence No. 7: FIG. 7), and the resulting PCR product was cleaved with NsiI to obtain a DNA fragment of approximately 2 kbp containing a ColE1 ori region as an origin of replication of Escherichia coli and an ampicillin resistance gene.

PCR was conducted such that a PCR kit (made by Takara Shuzo Co., Ltd.) was used, 100 pmol of each primer, 2.5 units of a Taq polymerase, 200 μM dNTP, 1 ng pUC119 template DNA and 100 μl Taq buffer (10 mM Tris-hydrochloride (pH 8.5), 2.5 mM Mg⁺⁺, 50 mM potassium chloride and 100 μg/ml bovine serum albumin) were mixed, the mixture was maintained at 96° C. for 30 seconds, and a cycle of DNA thermal denaturation (94° C., 60 sec), primer annealing (54° C., 60 sec) and primer elongation (70° C., 60 sec) was then repeated 25 times. This condition is hereinafter referred to as condition 1.

The above-obtained DNA fragment of approximately 2 kbp was ligated to an Sse8387I site of plasmid vector pNY301 (JP-A 10-295376 (1998)) containing a P5 promoter from an HWP promoter region of Brevibacillus choshinensis HPD3 1 and a natural type HWP signal sequence as a secretion signal sequence with a T4 DNA ligase using a DNA ligation kit (made by Takara Shuzo Co., Ltd.). E. coli JM109 (made by Takara Shuzo Co., Ltd.) was transformed with this DNA by the CaCl2 method (Molecular Cloning 2nd ed., A Laboratory Manual, Cold Spring Harbor Laboratory, 1, 82, (1989)), and a plasmid was extracted from the resulting ampicillin resistance transformant. The resulting plasmid was a novel plasmid shuttle vector replicable in Escherichia coli and bacteria of the genus Brevibacillus, and was designated pNC301.

Plasmid shuttle vector pNC301contains the P5 promoter from the HWP promoter region of Brevibacillus choshinensis HPD31, the neomycin resistance gene as a selective marker gene for the genus Brevibacillus, the ColE1 ori region as an origin of replication of Escherichia coli and the ampicillin resistance gene as a selective marker gene for Escherichia coli. It contains further the natural type HWP signal sequence as a secretion signal sequence (FIG. 22).

Construction of plasmid shuttle vector pNCMO2 is described below by referring to FIG. 23.

(2) Construction of Plasmid pNC

The total length of pNC301 obtained by excluding from plasmid shuttle vector pNC301 the HWP promoter region from Brevibacillus choshinensis HPD31 was amplified by PCR under condition 1 using primer 3 (Sequence No. 8: FIG. 8) and primer 4 (Sequence No. 9: FIG. 9). The amplified fragment of approximately 5 kbp was treated with BclI, and subjected to self-ligation with a T4 DNA ligase. E. coli JM109 was transformed with this DNA by the CaCl₂ method to obtain plasmid pNC. The reaction condition of PCR was (a cycle of a denaturation temperature: 94° C.-60 sec, an annealing temperature: 54° C.-120 sec and a DNA chain elongation temperature: 70° C.-180 sec was repeated 25 times).

(3) Construction of Plasmid pGEM-TP2

A DNA sequence encoding a P2 promoter from an HWP promoter region contained in plasmid pNU210 (Udaka, S. et al., Methods In Enzymology, 217, 23-33 (1993)) was amplified by PCR under condition 1 using primer 5 (Sequence No. 10: FIG. 10) and primer 6 (Sequence No. 11: FIG. 11) to obtain a DNA fragment of approximately 140 bp. Since primer 6 contains a lac operator sequence, this DNA fragment contains the lac operator sequence at the 3′-terminus of the P2 promoter. This fragment was ligated to pGEM-T (made by Promega) with a T4 DNA ligase. E. coli JM109 was transformed with this DNA by the CaCl₂ method, and a plasmid was extracted from the resulting ampicillin resistance transformant to obtain pGEM-TP2.

(4) Construction of Plasmid pGEM-TP2⁺

A DNA sequence contained in plasmid pNH326 (Kajino, T., et al., Appl. Environ, Microbiol., 66, 638-642 (2000)), which contains SD1 and SD2 sequences of an HWP promoter region of Brevibacillus choshinensis HPD31, an R2L6 type modified HWP signal sequence (JP-A 7-170984 (1995))(Sequence No. 5, Sequence No. 21: FIG. 5) as a secretion signal sequence and a multicloning site, was amplified by PCR under condition 1 using primer 7 (Sequence No. 12: FIG. 12) and primer 8 (Sequence No. 13: FIG. 13) to obtain a DNA fragment of approximately 270 bp. The resulting DNA fragment was treated with restriction endonucleases NsiI and HindIII, and ligated to a PstI/HindIII site of pGEM-TP2 with a T4DNA ligase. E. coli JM109 was transformed with this DNA by the competent cell method to obtain pGEM-TP2+.

(5) Construction of Plasmid Shuttle Vector pNCMO2

Further, pGEM-TP2 +was treated with BamHI and PstI. The resulting fragment of approximately 400 bp was inserted into a BclI/PstI site of pNC, ligated with a T4 DNA ligase, and E. coli JM109 was transformed with this DNA by the CaCl2 method. A plasmid was extracted from the resulting ampicillin resistant transformant to obtain novel plasmid shuttle vector pNCMO2 (FIG. 23). The construction outline of plasmid shuttle vector pNCMO2 is shown in FIGS. 22 and 23. The restriction map of the thus-obtained novel plasmid shuttle vector pNCMO2 and the nucleotide sequence of its part containing a promoter and the like were shown in FIG. 21. In the above-mentioned manner, Brevibacillus choshinensis HPD31-S5 (FERM BP-6623) was transformed using this plasmid shuttle vector, and the resulting transformant (Brevibacillus choshinensis HPD31-S5/pNCMO2) was internationally deposited as FERM BP-7394.

Example 2

Transformation Efficiency of pNCMO2 and pNC301

A transformation efficiency of pNCMO2 and pNC301 is shown in Table 1. The transformation efficiency of both vectors to E. coli JM109 was satisfactorily high. The transformation efficiency of pNCMO2 to Brevibacillus choshinensis HPD31-S5 was low, as compared with that of pNC301, but high enough to insert the constructed plasmid. The transformation of E. coli JM109 was performed by the CaCl₂ method (Molecular Cloning, Cold Spring Harbor Laboratory, Press, 1, 82, (1989)), and the transformation of Brevibacillus choshinensis HPD31-S5 was performed by electroporation (Takagi, H. et al., Agric. Biol. Chem., 53, 3099-3100 (1989)). The electroporation was performed under conditions of 1.5 kV, 1000 Ω, 25 μF and 1.8 msec using Gene Pulser (manufactured by BioRad).

TABLE 1 Transformation efficiency of pNCMO2 and pNC301 Transformation efficiency Plasmid vector Host bacterium (CFU/μgDNA) pNOMO2 E. coli JM109 6.1 × 10⁶ pNC301 E. coli JM109 8.6 × 10⁶ pUC119 E. coli JM109 1.9 × 10⁷ pNCMO2 Brevibacillus choshinensis HPD31-S5 5.2 × 10⁴ pNC301 Brevibacillus choshinensis HPD31-S5 1.2 × 10⁶ pNY301 Brevibacillus choshinensis HPD31-S5 1.9 × 10⁶

Example 3

Comparison of BLA Production Between Plasmid Shuttle Vector pNCMO2 and Plasmid Shuttle Vector pNC301

(1) Construction of Recombinant Gene Expression Plasmids pNCMO2BLA and pNC301BLA

An α-amylase (BLA) gene from Bacillus licheniformis was amplified by PCR with pHY4631 (Yamagata, H. et al., J. of Biotechnol, 169, 1239-1245 (1987)) as a template using primer 9 (Sequence No. 14: FIG. 14) and primer 10 (Sequence No. 15: FIG. 15). The resulting PCR product was digested with restriction endonucleases PstI and HindIII to obtain a BLA gene-containing DNA fragment of approximately 1.5 kb. Plasmid vectors pNCMO2 and pNC301 constructed in Example 1 were digested with restriction endonucleases PstI and HindIII, and the above-obtained BLA gene-containing fragment was ligated thereto with a T4DNA ligase to obtain plasmid vectors pNCMO2BLA and pNC301BLA (FIG. 24). Further, E. coli JM109 was transformed by the CaCl₂ method using plasmid vectors pNCMO2BLA and pNC301BLA to obtain transformants E. coli JM109/pNCMO2BLA and E. coli JM109/pNC301BLA carrying plasmid vectors pNCMO2BLA and pNC301BLA respectively.

Further, as a BLA gene, it was also possible to use a DNA fragment cleaved from a BLA gene-containing plasmid, for example, pHT110BLA (Japanese Patent No. 2727391).

(2) BLA Production with E. coli JM109/pNCMO2BLA and E. coli JM109/pNC301BLA

Each of the transformants was inoculated to 1.5 ml portion of 2×YT medium, an incubated overnight at 37° C. with shaking. This culture solution was treated with a sonicator for 30 seconds to disrupt the cells, and the amylase activity in the treated solution was measured by the Saito's-method (Arch. Biochem. Biophys., 155, 290 (1973)) using a soluble starch as a substrate (FIG. 25). E. coli JM109/pNCMO2BLA produced amylase in an amount which was approximately 1/70 in comparison to E. coli JM109/pNC301BLA, and the gene expression in Escherichia coli was efficiently suppressed.

Further, E. coli JM109/pNCMO2BLA and E. coli JM109/pNC301BLA were inoculated on an LA agar medium containing 3% starch, and incubated overnight at 37+ C. to form colonies, and a halo formability and growth thereof were compared (FIG. 26: photo in place of a drawing). As a result, E. coli JM109/pNCMO2BLA was smaller in size of the halo around the colony than E. coli JM109/pNC301BLA, and the BLA expression was therefore suppressed. Moreover, from the size of the colony grown, it was found that E. coli JM109/pNCMO2BLA was proliferated faster. This is presumably because the BLA expression was suppressed at good efficiency in E. coli JM109/pNCMO2BLA and the stress exerted on the bacteria was therefore reduced to improve the amplification.

When E. coli JM109/pNCMO2BLA was incubated on an agar medium containing 1 mM IPTG, the size of the halo formed was almost the same as that of the halo formed with the same strain incubated on a IPTG-free agar medium (FIG. 27: photo in place of a drawing). With respect to the expression suppressing effect in Escherichia coli provided by pNCMO2, this is presumably because in addition to the suppressing effect by inserting the lac operator, the P2 promoter activity is quite low in Escherichia coli, as compared with the P5 promoter activity.

(3) BLA Production with Brevibacillus choshinensis HPD31-S5/pNCMO2BLA and Brevibacillus choshinensis HPD31S5/pNC301BLA

Brevibacillus choshinensis HPD31-S5 was transformed by electroporation with plasmid vectors pNCMO2BLA and pNC301BLA obtained in (1) respectively to obtain transformants Brevibacillus choshinensis HPD31-S5/pNCMO2BLA and Brevibacillus choshinensis HPD31-S5/pNC301BLA carrying plasmid vectors pNCMO2BLA and pNC301BLA respectively (FIG. 24). The electroporation was performed under conditions of 1.5 kV, 1,000 Ω, 25 μF and 1.8 msec using Gene Pulser (manufactured by BioRad). Each of the transformants was inoculated in a test tube containing 1.5 ml TMN medium, and incubated at 30° C. for 2 days with shaking. This culture solution was centrifuged, and the amylase activity of the culture supernatant was measured by the Saito's method (Arch. Biochem. Biophys., 155, 290 (1973)) using a soluble starch as a substrate (FIG. 28). Brevibacillus choshinensis HPD31-S5/pNCMO2BLA produced amylase in an amount which was approximately 22 times as large as Brevibacillus choshinensis HPD31-S5/pNC301BLA. Consequently, it was shown that pNCMO2 can express a gene in bacteria of the genus Brevibacillus far more efficiently than pNC301.

Example 4

Construction of Recombinant Gene Expression Plasmid pNY326CT

(1) Obtainment of CTA Gene and CTB Gene

A cholera toxin (CT) A subunit gene (CTA)(0.7 bp) was amplified by PCR with a Vibrio cholerae chromosomal DNA (Mekalanos, J. et al., Nature, 306, 551-557 (1983)) as a template using two synthetic primers, primer 11 (Sequence No. 16: FIG. 16) and primer 12 (Sequence No. 17: FIG. 17). In like manner, a CT B subunit gene (CTB)(0.3 bp) was amplified using two primers, primer 13 (Sequence No. 18: FIG. 18) and primer 14 (Sequence No. 19: FIG. 19).

(2) Plasmid pT7BlueCTA and plasmid pT7BlueCTB

Plasmid pT7Blue (made by Novagen) and the above-obtained CTA gene or CTB gene were ligated with a T4 ligase to obtain plasmid pT7BlueCTA carrying the CTA gene or plasmid pT7BlueCTB carrying the CTB gene.

(3) Construction of Plasmid pNY326CTA

Plasmid pNY326 [plasmid obtained by converting the signal sequence of pNY301(JP-A 10-295378 (1998)) to an R2L6 type (Sequence Nos. 5, 21: FIG. 5)] was treated with NcoI and HindIII to obtain a fragment of 3.6 kbp. Further, pT7BlueCTA was treated with NcoI and HindIII to obtain a CTA gene-containing DNA fragment of 0.7 kbp. This DNA fragment was ligated to the above-obtained gene fragment of 3.6 kbp with a T4 DNA ligase. Brevibacillus choshinensis HPD31-S5 was transformed by electroporation using the ligated DNA. From the resulting neomycin resistant strain, a plasmid was extracted to obtain pNY326CTA carrying the CTA gene.

(4) Construction of Plasmid pNY326CTB

In like manner, pNY326 was treated with NcoI and BamHI to obtain a DNA fragment of 3.6 kbp. Further, pT7BlueCTB was treated with NcoI and BamHI to obtain a CTB gene-containing DNA fragment of 0.3 kbp. This DNA fragment was ligated to the above-obtained DNA fragment of 3.6 kbp with a T4 DNA ligase. Brevibacillus choshinensis HPD31-S5 was transformed using the ligated DNA to select a strain having a neomycin resistance. From the selected strain, a plasmid was extracted to obtain plasmid pNY326 CTB carrying the CTB gene.

(5) Trial of Transformation of Brevibacillus choshinensis HPD31-S5 with pNY326CT

pNY326CTB was treated with BamHI and HindIII to obtain a DNA fragment of 4.7 kbp. Further, a CTA gene in the form containing a SD2 sequence (SD-CTA gene (0.8 kbp)) was amplified by PCR with pNY326CTA as a template using two primers, primer 15 (Sequence No. 20: FIG. 20) and primer 11 (Sequence No. 16: FIG. 16). The PCR product was treated with BamHI and HindIII to obtain a fragment of 0.4 kbp. This fragment was ligated to the above-obtained DNA fragment of 4.7 kbp from pNY326CTB with a T4 DNA ligase. Brevibacillus choshinensis HPD31-S5 was transformed by electroporation using the ligated DNA, and the transformant was spread on a 50 μg/ml neomycin-containing TM agar medium (1% peptone, 0.2% yeast extract, 0.5% meat extract, 1% glucose, 0.001% FeSO₄.7H₂O, 0.001% MnSO₄.4H₂O, 0.0001% ZnSO₄.7H₂O, 1.5% agar, pH 7.0) to try to select a strain having a neomycin resistance. However, the resistant strain was not obtained. The electroporation was performed under conditions of 1.5 kV, 1,000 Ω, 25 μF and 1.8 msec using Gene Pulser (manufactured by BioRad).

Example 5

Construction of Recombinant Gene Expression Plasmid pNCMO2CT

(1) Construction of Plasmid pNCMO2CTB

pNCMO2 was treated with NcoI and BamHI to obtain a fragment of 5.2 kbp. Further, pT7BlueCTB was treated with NcoI and BamHI to obtain a CTB gene-containing DNA fragment of 0.3 kbp. This DNA fragment was ligated to the above-obtained gene fragment of 5.2 kbp with a T4 DNA ligase (FIG. 29). E. coli JM109 was transformed with this ligated DNA, and a plasmid was extracted to obtain pNCMO2CTB carrying the CTB gene.

(2) Construction of Plasmid pNCMO2CT

pNCMO2 CTB was treated with BamHI and HindIII to obtain a fragment of 5.5 kbp. The SD-CTA gene (0.8 kbp) obtained in Example 4 (5) was treated with BamHI and HindIII to recover a fragment of 0.8 kbp. This fragment was ligated to the above-obtained gene fragment of 5.5 kbp with a T4 DNA ligase (FIG. 29). E. coli JM109 was transformed with the ligated DNA to select a transformant having an ampicillin resistance. From the three selected transformants, a plasmid was extracted to obtain plasmid pNCMO2CT carrying the CTB gene. As a result of sequencing, it was found that in all of the transformants, the CTB gene was correctly ligated to the plasmid. The transformants obtained here were designated E. coli JM109/pNCMO2CT. Brevibacillus choshinensis HPD31-S5 was transformed with pNCMO2CT extracted from E. coli JM109/pNCMO2CT by electroporation. Consequently, a large number of transformants carrying the same plasmid were obtained. The resulting transformants were designated Brevibacillus choshinensis HPD31-S5/pNCMO2CT. The electroporation was performed under conditions of 1.5 kV, 1,000 Ω, 25 μF and 1.8 msec using Gene Pulser (manufactured by BioRad).

(3) Expression of CT with Brevibacillus choshinensis HPD31-S5/pNCMO2CT

Brevibacillus choshinensis HPD31-S5/pNCMO2CT was cultured in 3 ml of a 50 μg/ml neomycin-containing TM liquid medium at 30° C. for 2 days using a medium-sized test tube while being shaken, and the culture supernatant was subjected to SDS-PAGE. The analysis was conducted by Coomassie Brilliant Blue staining and western blotting with a rabbit CT polyclonal antibody. The estimated molecular weights of CTA and CTB were 28 kDa and 12 kDa respectively, and showed staining bands in positions of corresponding molecular weights respectively. From the color depths of the bands, the secretory production amount of CTA was estimated at 70 mg/l and the secretory production amount of CTB at 30 mg/l respectively. Its SDS-PAGE electrophoresis pattern is shown in a photo in place of a drawing (FIG. 30). Further, when the culture supernatant was purified using a galactose resin specifically binding CT (Microbial Pathogenesis, 16, 71-79 (1994)) and the purified fraction was then subjected to electrophoresis without being heat-treated, the band was shifted to a site of approximately 90 kDa. From this fact, it was presumed that the expressed subunit took a 1A5B structure.

Effects of the Invention

According to the invention, the plasmid shuttle vector between Escherichia coli and bacteria of the genus Brevibacillus is provided. Further, the plasmid shuttle vector of the invention, as shown in the results of the expression of the BLA gene in Example 3, suppresses the gene expression in Escherichia coli and can allow the efficient gene expression in Brevibacillus choshinensis. As shown by the expression of CT in Examples 4 and 5, plasmid shuttle vector pNCMO2 in the invention is useful especially for construction of the recombinant gene expression plasmid requiring complex gene construction and for protein production with the transformant transformed with the said recombinant gene expression plasmid.

Description on Microorganisms Deposited Under Rule 13-2

1. Brevibacillus choshinensis HPD31-S5/pNCMO2

-   -   a. Name and address of a depositary agency in which this         microorganism was deposited     -   Name: International Patent Organism Depositary, National         Institute of Advanced Industrial Science and Technology     -   Address: AIST Tsukuba Central 6, 1-1-1 Higashi, Tsukuba Ibaraki,         305-8566, Japan     -   b. Date on which the microorganism was deposited in the         depositary agency of a Dec. 12, 2000     -   c. Receipt Number that the depositary agency of a assigned on         the deposition FERM BP-7394

2. Brevibacillus choshinensis HPD31 (FERM BP-1087)

-   -   a. Name and address of a depositary agency in which this         microorganism was deposited     -   Name: International Patent Organism Depositary, National         Institute of Advanced Industrial Science and Technology     -   Address: AIST Tsukuba Central 6, 1-1-1 Higashi, Tsukuba Ibaraki,         305-8566, Japan     -   b. Date on which the microorganism was deposited in the         depositary agency of a Aug. 31, 1999     -   c. Receipt Number that the depositary agency of a assigned on         the deposition FERM BP-6863 

1. A plasmid shuttle vector replicable in both Brevibacillus choshinensis and Escherichia coli, wherein said plasmid shuttle vector comprises the following DNA sequences: (1) an origin sequence of replication functionable in Escherichia coli; (2) an origin sequence of replication functionable in Brevibacillus choshinensis; (3) a P2 promoter sequence; (4) a lac operator sequence; (5) an SD1 sequence; (6) an SD2 sequence; (7) a secretion signal sequence; (8) a multicloning site sequence; (9) an HS gene sequence; (10) a Rep protein gene; and (11) one member selected from the group consisting of the following members (a) and (b): (a) a drug resistance gene functionable as a selective marker in Brevibacillus choshinensis, and a drug resistance gene functionable as a selective marker in Escherichia coli; and (b) a zeocin resistance gene, wherein a region comprising the DNA sequences (3)-(9) has a DNA sequence according to SEQ ID NO:
 22. 2. The plasmid shuttle vector according to claim 1, wherein the drug resistance gene functionable as a selective marker in Brevibacillus choshinensis in member (a) of DNA sequence (11) is one member selected from the group consisting of a neomycin resistance gene and an erythromycin resistance gene, and the drug resistance gene functionable as a selective marker in Escherichia coli in member (a) of DNA sequence (11) is one member selected from the group consisting of a kanamycin resistance gene, an ampicillin resistance gene, and a chloramphenicol resistance gene.
 3. A plasmid shuffle vector pNCMO2 comprising SEQ ID NO: 22 having the following restriction endonuclease recognition sequence sites:


4. A DNA sequence according to SEQ ID NO:
 22. 5. A transformant obtained by transforming Brevibacillus choshinensis with a recombinant plasmid obtained by inserting a DNA sequence encoding a protein into the plasmid shuttle vector according to claim
 1. 6. A transformant obtained by transforming Brevibacillus choshinensis with a recombinant plasmid obtained by inserting a DNA sequence encoding a protein into the plasmid shuttle vector according to claim
 2. 7. A transformant obtained by transforming Brevibacillus choshinensis with a recombinant plasmid obtained by inserting a DNA sequence encoding a protein into the plasmid shuttle vector pNCMO2 according to claim
 3. 8. A process for producing a protein, wherein said process comprises: culturing the transformant according to claim 5 in a medium; and collecting the protein secreted and accumulated in the medium. 